Molding apparatus

ABSTRACT

By arranging such that the crystal fractures of alloy raw meal powder having crystal orientational relationship with one another get combined in the magnetic field, there is provided a molding apparatus which is capable of molding a molded body having an extremely high orientation. The molding apparatus of this invention has: a cavity for filling thereinto a powder that is polarized in magnetic field or electric field; means for generating magnetic field or electric field capable of charging the powder filled in the cavity with the magnetic field or electric field; an agitating means for agitating the powder in a state of being charged with the magnetic field or the electric field, thereby orienting the powder; and a pressurizing means for applying a compression force in the magnetic field or electric field to the agitated and oriented product.

This application is a national phase entry under 35 U.S.C. §371 of PCTPatent Application No. PCT/JP2007/73480, filed on Dec. 5, 2007, whichclaims priority under 35 U.S.C. § 119 to Japanese Patent Application No.2007-003401, filed Jan. 11, 2007, both of which are incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to a molding apparatus for manufacturing amolded body by compression-molding a powder and relates, in particular,to a molding apparatus to be used in manufacturing a rare-earthpermanent magnet such as a Nd—Fe—B system permanent magnet.

BACKGROUND ART

Rare-earth permanent magnets, particularly Nd—Fe—B sintered magnets(so-called neodymium magnet) are made of a combination of iron withelements of Nd and B that are low-priced and abundant as naturalresources and also capable of stable supply, and can therefore bemanufactured at a low cost and, at the same time, have high magneticproperties (maximum energy product is about 10 times that of ferriticmagnets). Therefore, they are used in various kinds of electronicproducts and are recently widely used in motors and generators forhybrid cars.

As an example of manufacturing Nd—Fe—B sintered magnets, there is knowna powder metallurgy method. In this method, Nd, Fe and B are first mixedin a predetermined composition ratio, dissolved, and molded tomanufacture an alloy raw material. It is once coarsely crushed by, e.g.,hydrogen crushing step, and is subsequently finely ground by, e.g., jetmill fine grinding step, thereby obtaining an alloy raw meal powder.Then, the obtained alloy raw meal powder is subjected to orientation inthe magnetic field (magnetic field orientation), and iscompression-molded while being charged with magnetic field, therebyobtaining a molded body. Then, the molded body is sintered underpredetermined conditions to thereby manufacture a sintered magnet.

As a method of compression molding in the magnetic field, there isgenerally used a uniaxial pressurizing type of compression moldingapparatus. In this compression molding apparatus, alloy raw meal powderis filled into a cavity formed in a penetrating hole in a die, and ispressurized (pressed) by a pair of upper and lower punches from theupper and lower directions to thereby form a product out of the alloyraw meal powder. However, at the time of compression molding by means ofthe pair of punches, high orientation cannot be obtained, and theimprovement in the magnetic properties cannot be attained, due to thefriction among the particles of the alloy raw meal powder and due to thefriction between the alloy raw meal powder and the wall surface of themold set in position in the punch. In view of the above, there is knownanother compression molding apparatus in which, after having filled acavity with alloy raw meal powder, at least one of punches of an upperpunch and a lower punch is vibrated in the direction of pressurizing(pressing direction) at the time of magnetic field orientation (seepatent document 1).

Patent Document 1: International Publication No. 2002-60677, see e.g.,claims)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in the above-described compression molding apparatus, sincevibration is caused to take place only by one of the upper punch and thelower punches at the time of magnetic field orientation, the positionalrelationship among the particles of the alloy raw meal powder within thecavity hardly changes from the state in which it was initially filledinto the cavity. As a result, in case the crystal fractures of theadjoining particles in the orientation direction of the magnetic fielddo not match with each other (since alloy raw meal powder of Nd—Fe—Bsintered magnet is manufactured by mixing Nd, Fe and B and fusing andalloying and thereafter grinding them, the surface of the alloy raw mealpowder has formed therein crystal fractures), clearance will remain, inthe end, among the particles of the alloy raw meal powder and,therefore, the easy axis of magnetization of the alloy raw meal powderwill not be in order. If compression molding is executed in this state,there is a problem in that the orientation will get out of order.

In view of the above points, this invention has an object of providing amolding apparatus which is constituted to be able to obtain a moldedbody of extremely high orientation by arranging such that the crystalfractures of the powder having more equal crystal orientationalrelationship can be combined together.

Means for Solving the Problems

In order to solve the above problems, the molding apparatus according toclaim 1 comprises: a filling chamber filled with powder that ispolarized in one of magnetic field and electric field; means forgenerating one of magnetic field and electric field so as to enable tocharge the powder filled in the filling chamber with one of the magneticfield and electric field; an agitating means for agitating and orientingthe powder in a state of being charged with one of the magnetic fieldand electric field; and a pressurizing means for applying a compressionforce in one of the magnetic field and electric field to the powder thathas been agitated and oriented, thereby molding the powder.

According to this invention, since the powder filled in the fillingchamber can be agitated and oriented by the agitating means in themagnetic field or electric field, the positional relationship among theparticles of the powder in the filling chamber will be changed from thestate in which the powder was initially filled into the filling chamber.As a result, there will be more chances in which, among the combinationsof crystal fractures in orienting in the magnetic field or electricfield, the crystal fractures having more equal crystal orientationalrelationship get bonded. Once the crystal fractures having equal crystalorientational relationship are bonded, there will be formed firm bondingchains and, as a result, the crystal fractures get combined and arrayedwithout clearance in the magnetic field orientation. Then, the powdercan be molded by the pressuring means under compression in a state inwhich the crystal fractures having equal crystal orientationalrelationship get combined together, there can be obtained a molded bodyhaving a high orientation. At the same time, since the crystal fractureshaving equal orientational relationship are firmly bonded together,there can be obtained a molded body of high density at a lower moldingpressure. As a result, the strength of the molded body increases and therate of occurrence of rejection can be lowered.

If the agitating means is the agitating means is disposed in a manner tobe movable into and out of the filling chamber, the workability forobtaining the molded body by compression-molding the powder canadvantageously be improved.

If the filling chamber has an opening for filling the powdertherethrough, and a lid body is provided integral with the agitatingmeans in a manner to close the opening when the agitating means is movedinto the filling chamber, the powder can be prevented from splashing outof the filling chamber during agitation.

If the agitating means is constituted by a non-magnetic material, when,e.g., alloy raw meal powder for a permanent magnet is agitated in themagnetic field, the magnetic field can be prevented from gettingdisturbed due to adhesion of the alloy raw meal powder to the agitatingmeans and due to consequent insufficient agitation of the alloy raw mealpowder.

The means for generating the magnetic field shall preferably be capableof generating static magnetic field in a range of magnetic fieldintensity of 5˜30 kOe. When a rare-earth permanent magnet ismanufactured, if the intensity of the magnetic field is below 5 kOe, apermanent magnet of high orientation and high magnetic properties cannotbe obtained. If the intensity of the magnetic field is above 30 kOe, themagnetic field generating apparatus becomes too large, and thedurability of the apparatus becomes poor, which is not practical.

On the other hand, the means for generating the magnetic field may bearranged to be capable of generating magnetic pulse field in a range ofmagnetic field intensity of 5˜50 kOe. According to this configuration,it is possible to cause the powder itself that has been filled in thefilling chamber to be vibrated, thereby further improving theorientation. However, if the intensity of the magnetic field is below 5kOe, there cannot be obtained a permanent magnet having high orientationand high magnetic properties. If the intensity of the magnetic field isabove 50 kOe, the magnetic field generating apparatus becomes too large,and the durability of the apparatus becomes poor, which is notpractical.

The above-described powder is alloy raw meal powder for rare-earthmagnet and the alloy raw meal powder is manufactured by quenchingmethod. According to this configuration, the alloy raw meal powderbecomes angular particulate shape, whereby the area of a single crystalfracture can be made large and the clearance among the particles of thealloy raw meal powder can be made small. By thus improving theflowability of the alloy raw meal powder, the chances become furtherincreased in which the crystal fractures of the alloy raw meal powderhaving more equal crystal orientational relationship get combined withone another. In addition thereto, the orientation can further beimproved. As a result, by using the molding apparatus of this invention,there can be obtained a permanent magnet that is high in density withoutdisturbance in orientation and that is high in magnetic properties.

EFFECT OF THE INVENTION

As described hereinabove, according to the molding apparatus of thisinvention, there can be obtained an effect in that crystal fractures ofthe powder having more equal crystal orientational relationship in themagnetic field or in the electric field are arranged to get combined,thereby manufacturing a molded body of an extremely high orientation.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to FIGS. 1 through 5, reference numeral 1 denotes amolding apparatus according to this invention. The molding apparatus 1is suitable for manufacturing rare earth permanent magnet, inparticular, Nd—Fe—B sintered magnet (inclusive of oriented body andmolded body). The molding apparatus 1 is a compression molding apparatusof a uniaxial pressurizing type in which the direction of pressurizing(pressing direction) is vertical to the direction of magneticorientation, and has a base plate 12 which is supported by leg pieces11. Above the base plate 12 there is disposed a die 2. The die 2 issupported by a plurality of supporting columns 13 which penetratethrough the base plate 12. The other end of each of the supportingcolumns 13 is connected to a connecting plate 14 disposed below the baseplate 12. The connecting plate 14 is connected to a driving means, e.g.,a cylinder rod 15 of a hydraulic cylinder of a known construction.According to this configuration, when the lower hydraulic cylinder isactuated to move up and down the connection plate 14, the die 2 ismovable in an up-and-down direction (pressurizing direction Y).

In substantially the central part of the die 2, there is formed apenetrating hole 21 in the up-and-down direction. Into the penetratinghole 21 there can be inserted a lower punch 31 which is verticallydisposed on substantially the central part of the upper surface of thebase plate 12. When the lower hydraulic cylinder is actuated to lowerthe die 2, the lower punch 31 is inserted into the penetrating hole 21to thereby define a cavity (filling chamber) 22 inside the penetratinghole 21. Relative to the cavity 22 a powder feeding apparatus (notillustrated) of the known construction is movable back and forth. Bymeans of this powder feeding apparatus there can be filled an alloy rawmeal powder metered in advance into the cavity 22.

On an upper part of the die 2 there is disposed a die base 16 which liesopposite to the base plate 12. On a lower surface of the die base 16there is provided an upper punch 32 in a position capable of insertioninto the cavity 22. A vertically disposed pair of the upper punch 32 andthe lower punch 31 constitutes the pressuring means. Further, at thecorner portions of the die base 16 there are formed penetrating holes inthe vertical direction. In each of the penetrating holes there isinserted a guide rod 17 one end of which is fixed to the upper surfaceof the die 2. To the upper surface of the die base 16 there is connecteda driving means, e.g., a cylinder rod 18 of a hydraulic cylinder (notillustrated) of a known construction. When this hydraulic cylinder isactuated, the die base 16 is ready to be moveable up and down guided bythe guide rods 17 and consequently the upper punch 32 becomes movable inthe vertical direction (pressurizing direction) so that the upper punch32 can be inserted into the penetrating hole 21 of the verticallymovable die 2. According to this configuration, at the time ofcompression molding, a compression force is applied to the alloy rawmeal powder P for molding by the pair of the upper and lower punches 31,32 within the cavity 22, whereby a molded body of a predetermined shapecan be obtained (molding step).

In addition, on a periphery of the die 2 there is provided a magneticfield generating apparatus 4 in order to orient in the magnetic fieldthe alloy raw meal powder P inside the cavity 22. The magnetic fieldgenerating apparatus 4 is disposed in a symmetrical manner so as tosandwich the die 2 from both sides, and has a pair of yokes 41 a, 41 bmade of a material that is high in magnetic permeability such as mildsteel, pure iron, permendur, and the like. Both the yokes 41 a, 41 bhave wound thereabout coils 42 a, 42 b and, by charging each of thecoils 42 a, 42 b with electric power, there will be generated staticmagnetic field in a direction X perpendicular to the pressurizingdirection (up-and-down direction Y). According to this configuration,the alloy raw meal powder P filled in the cavity 22 can be oriented.

The alloy raw meal powder P that is a power polarized in the magneticfield is manufactured in the following manner. In other words, Fe, B,and Nd are blended in a predetermined composition ratio, and an alloy of0.05 mm ˜0.5 mm is first manufactured by a quenching process, e.g., by astrip cast method. On the other hand, an alloy of about 5 mm thick mayalso be manufactured by a centrifugal casting method, or else a smallamount of Cu, Zr, Dy, Al or Ga may be added at the time of blending.Then, the manufactured alloy is coarsely crushed by a known hydrogencrushing step and is subsequently finely ground by a jet mill finecrushing step in nitrogen gas atmosphere, thereby obtaining alloy rawmeal powder of an average particle size of 2-10 μm. In this case, if thequenching process is used, the alloy raw meal powder P becomes angularparticle shape, each crystal fracture area can be made large, and theclearance among the particles of the alloy raw meal powder P can be madesmall.

In order to improve the flowability, preferably a lubricant is added ina predetermined mixing ratio to the alloy raw meal powder P manufacturedas described above. The surface of the alloy raw meal powder P is coatedwith this lubricant. As the lubricant, solid lubricants or liquidlubricants having a low viscosity are used so that they do not damagethe metal mold. As the solid lubricants, there can be listed lamellarcompounds (MoS₂, WS₂, MoSe, graphite, BN, CFx, and the like), soft metal(Zn, Pb, and the like), rigid materials (diamond powder, TiN powder, andthe like), organic high polymers (PTEE series, aliphatic nylon series,higher aliphatic series, fatty acid amide series, fatty acid esterseries, metallic soap series, and the like). It is particularlypreferable to use zinc stearate, ethylene amide, and grease offluoroether series.

On the other hand, as the liquid lubricant, there can be listed naturalgrease material (vegetable oils such as castor oil, coconut oil, palmoil, and the like; mineral oils; petroleum grease; and the like), andorganic low molecular materials (low-grade aliphatic series, low-gradefatty acid amide series, low-grade fatty acid ester series). It isparticularly preferable to use liquid fatty acid, liquid fatty acidester, and liquid fluorine lubricant. Liquid lubricants are used withsurfactant or by diluting with solvent. The carbon residue content ofthe lubricants that remains after sintering lowers the coercive force ofthe magnet. Therefore, it is preferable to use low molecular weightmaterials to facilitate the removal in the sintering step.

In case a solid lubricant is added to the alloy raw meal powder P,addition may be made in a mixing ratio of 0.02 wt %˜0.1 wt %. If themixing ratio is less than 0.02 wt %, the flowability of the alloy rawmeal powder P will not be improved and, consequently, the orientationwill not be improved. On the other hand, if the mixing ration exceeds0.1 wt %, the coercive force lowers under the influence of the carbonresidue content that remains in the sintered magnet when the sinteredmagnet is obtained. Further, in case a liquid lubricant is added to thealloy raw meal powder P, it may be added in a range of 0.05 wt %˜5 wt %.If the mixing ratio is less than 0.05 wt %, the flowability of the alloyraw meal powder P will not be improved and, consequently, there is apossibility that the orientation will not be improved. On the otherhand, if the mixing ration exceeds 5 wt %, the coercive force lowersunder the influence of the carbon residue content that remains in thesintered magnet when the sintered magnet is obtained. By the way, as thelubricants, if both the solid lubricant and the liquid lubricant areadded, the lubricants will be widely spread to every corner of the alloyraw meal powder P and, due to high lubricating effect, a higherorientation can be obtained.

After filling the cavity 22 formed in the penetrating hole 21 of the die2 with the alloy raw meal powder P manufactured as described above, thealloy raw meal powder P is compression-molded as a result ofpressurizing in the up-and-down direction by the pair of upper and lowerpunches 31, 32. At that time, it is necessary to enable to improve themagnetic properties by arranging such that a high orientation can beobtained. For that purpose, in this embodiment, there was provided themixing apparatus 5 that is movable into, and out of, the cavity 22. Themolding apparatus 1 is thus constituted as follows. That is, afterhaving filled the cavity 22 as the filling chamber with the alloy rawmeal powder P, prior to the compression molding (molding step) with thepair of upper and lower punches 31, 32, the alloy raw meal powder P inthe cavity 22 was arranged to be capable of being oriented (orientationstep), while agitating, in the magnetic field in a state in which staticmagnetic field is generated (in magnetic field) by electrically chargingeach of the coils 42 a, 42 b of the magnetic field generating apparatus4.

The agitating apparatus 5 has a supporting plate 51 provided on an uppersurface of the die 2 in parallel therewith. The upper surface of thesupporting plate 51 is provided with a hydraulic cylinder 52 of a knownconstruction. A pneumatically driven type of motor 53 of a knownconstruction is mounted on a cylinder rod 52 a that is projected to thelower side of the supporting plate 51. A rotary vane 54 is mounted(rotary agitation) on the motor 53 at a rotary shaft 53 a that isdisposed at a position on a longitudinal axial line of the cylinder rod52 a. The rotary shaft 53 a and the rotary vane 54 constitute theagitating means. The rotary vane 54 is of a screw vane type (propellervane). The rotary shaft 53 a and the rotary vane 54 are made of anon-magnetic material such as 18-8 stainless steel. By making the rotaryshaft 53 a and the rotary vane 54 in a non-magnetic material, at thetime of agitating the alloy raw meal powder in the magnetic field, thealloy raw meal powder P can be prevented from getting adhered to theagitating means, the adhesion causing insufficient agitation of thealloy raw meal powder P and consequent disturbance in the magneticfield.

The supporting plate 51 is mounted on two guide rails 55 elongated in adirection perpendicular to the up-and-down direction Y. By sliding thesupporting plate 51 along the guide rails 55, the agitating apparatus 5becomes capable of moving back and forth relative to the cavity 22. Inthis case, the powder feeding apparatus may also be mounted on the sameguide rails 55 so as to be freely moveable back and forth relative tothe cavity 22. Once the agitating apparatus stops at a stopper (notillustrated) provided on the guide rails 55, the rotary shaft 53 a ispositioned so as to be located on the longitudinal axis of the pair ofthe upper and lower punches 31, 32. A lid plate 56 made of anon-magnetic material is mounted on the rotary shaft 53 a of the motor53. Once the cylinder 52 is actuated to thereby lower the rotary vane 54to a predetermined position inside the cavity 22, the lid plate 56 comesinto abutment with the upper surface of the die 2 to thereby close theupper part of the penetrating hole 21. The lid plate 56 thus performsthe function of preventing the alloy raw meal powder P from jumping outto the outside of the cavity 22 during agitation.

According to this configuration, when the alloy raw meal powder P isoriented in the magnetic field, the flowability of the alloy raw mealpowder is improved by adding the lubricant to the alloy raw meal powderP, and the alloy raw meal powder P that is filled into the cavity 22 andis high in flowability is agitated while charging the alloy raw mealpowder with the magnetic field. As a result of the above, the positionalrelationship inside the cavity 22 among the particles of the alloy rawmeal powder P can be changed from the state at which it was initiallyfilled into the cavity 22. In combination therewith, as a combinedeffect, the chances of combining the crystal fractures of the alloy rawmeal powder P having more equal crystal orientational relationshipincrease. Once the crystal fractures having the same crystalorientational relationship get combined, strong bonding chains areformed, and the crystal fractures get joined together without clearancein the direction of magnetic orientation. By executing compressionmolding in this state, there can be obtained a high-density molded bodyM (see FIG. 5) without disturbance in the orientation. As a result ofincrease in the strength of the molded body, the rate of occurrence ofunacceptable products can be lowered and a molded body M (permanentmagnet) of high magnetic properties can be obtained. In this case, if aresin binder is mixed with the alloy raw meal powder P to be filled intothe cavity 22, rare earth bonded magnet (molded body) of high magneticproperties can be obtained.

Then, with reference to FIGS. 1 through 5, a description will be made ofthe manufacturing of Nd—Fe—B (Nd—Fe—B system) sintered magnet. First,from a waiting position in which each of the upper surfaces of the die 2and the lower punch 31 are flush with each other and in which the upperpunch 32 is positioned at the upper end (see FIG. 1), the hydrauliccylinder is actuated to raise the die 2 to a predetermined position sothat a cavity is defined inside the penetrating hole 21. Then, by thepowder feeding apparatus (not illustrated), the alloy raw meal powder Pthat has been weighed in advance and to which a lubricant has been mixedin a predetermined mixing ratio is filled into the cavity 22, and thepowder feeding apparatus is retreated. In this case, the chargingdensity of the alloy raw meal powder P in the cavity 22 is set to be2.2˜3.9 g/cc in order to prevent the alloy raw meal powder P fromgetting unbalanced or in order to leave freedom to move at the time ofagitation (see FIG. 2).

Then, the agitating apparatus 5 is moved so that the rotary shaft 53 aof the motor 53 is positioned on the longitudinal axis of the pair ofupper and lower punches 31, 32 (see FIG. 2). Then, the motor 53 and thelid plate 56 are lowered through the hydraulic cylinder 52. The lidplate 56 thus comes into abutment with the upper surface of the die 2,thereby blocking the upper surface of the penetrating hole 21. At thesame time, the rotary vane 54 is buried in the alloy raw meal powder Pfilled into the cavity 22 (see FIG. 3). In this state, the coils 42 a,42 b of the magnetic field generating apparatus 4 are charged withelectric power and, in the magnetic field, the motor 53 is actuated torotate the rotary vane 54 in the cavity 22 (orienting step). In thiscase, in order to obtain a high orientation, it is preferable to agitatewith the agitating apparatus 5 in the magnetic field of a range of 5kOe˜30 kOe, preferably, 10 kOe˜26 kOe. If the magnetic field intensityis weaker than 5 kOe or stronger than 30 kOe, a sintered magnet of highorientation and high magnetic properties cannot be obtained. Inaddition, in order for the alloy raw meal powder P filled into thecavity 22 to be mixed in its entirety, the number of rotation of therotary vane 54 is set to 100˜50000 rpm, preferably to 4000 rpm, and therotary vane is actuated for a predetermined period of time (1˜5seconds).

According to this configuration, even if the upper punch or the lowerpunch is subjected to vibrations as in the conventional method, in casethe crystal fracture of the raw meal powder particles P that lie next toone another in the direction of magnetic field orientation do not meeteach other, there will remain clearance among the alloy raw meal powderparticles P. This results in failure to array the alloy raw meal powderparticles P in the direction of the magnetic field orientation. If thecompression molding is performed in this state, the orientation getsdisturbed. Like in the embodiment, on the other hand, by orienting whileagitating the alloy raw meal powder P in a state in which the magneticfield is charged thereto, the positional relationship among theparticles of the alloy raw meal powder P within the cavity 22 will varyfrom the state in which the alloy raw meal powder was filled into thecavity 22. There will thus be many chances for the crystal fractures ofthe alloy raw meal powder P that has more equal crystal orientationalrelationship to be combined. Once the crystal fractures having equalcrystal orientational relationship get bonded with one another, therewill be formed a strong bonding chain. As shown in FIG. 4( b), thecrystal fractures get joined without clearance in the direction ofmagnetic orientation in a manner to form a bar-shape, thereby arrayingin the direction of orientation of the magnetic field.

Then, once the agitation of the alloy raw meal powder P in the magneticfield has been finished, the cylinder rod 52 a is lifted to the positionin which the rotary vane 54 is away upward of the die 2, and thereafterthe agitating apparatus 5 is slid along the guide rails 55 to therebyretract it. In this case, the electric charging to the coils 42 a, 42 bwill not be stopped. Then, the die base 16 is lowered to insert theupper punch 32 from the upper side into the penetrating hole 21. In astate in which the magnetic field is charged, compression molding of thealloy raw meal powder P inside the cavity 22 is started by the pair ofthe upper and lower punches 31, 32.

After a lapse of a predetermined time, the electric charging to thecoils 42 a, 42 b is stopped and, in this state, compression molding atthe maximum pressure will be executed. Finally, the upper punch 32 isgradually lifted to thereby gradually reduce the pressure. Thecompression molding is finished and the molded body M is formed (moldingstep). According to the above operations, compression molding isperformed in a state in which the alloy raw meal powder is joined in adirection of magnetic field orientation just like molding a bar shapewithout clearance among the crystal fractures so as to be in an array inthe magnetic field orientation. Therefore, there can be obtained ahigh-density molded body M (permanent magnet) without disturbance in theorientation, and the magnetic properties are also improved.

The molding pressure in the molding step is set to a range of 0.1˜1t/cm², more preferably to 0.2˜0.7 t/cm². At the molding pressure, e.g.,below 0.1 t/cm², the molded body does not have a sufficient strength.For example, it gives rise to cracks when the molded body is taken outof the cavity 22 of the molding apparatus. On the other hand, at amolding pressure exceeding 1 t/cm² a high pressure is exerted on thealloy raw meal powder P inside the cavity 22 and, as a result, moldingis made while orientation is struck out of shape and also there is apossibility that the molded body gives rise to cracks and splits. Inaddition, the intensity of the magnetic field in the molding step is setto a range of 5 kOe˜30 kOe. If the intensity of the magnetic field isweaker than 5 kOe, there cannot be obtained a product high inorientation and high in magnetic properties. On the other hand, if theintensity of the magnetic field is stronger than 50 kOe, the magneticfield generating apparatus becomes too large to be practical.

Subsequently, after having demagnetization by charging reverse magneticfield of, e.g., 3 kOe, the die 2 is lowered to the lower end. The moldedbody M inside the cavity 22 will then be pulled out to the upper surfaceof the die 16. The die base 16 is moved to thereby move the upper punch32 to the upper end, and then the molded body is taken out. Finally, theobtained molded body is contained in a sintering furnace (notillustrated) to execute sintering for a predetermined period of time ata predetermined temperature (1000° C.) in, e.g., Ar atmosphere(sintering step). Further, aging treatment is executed in Ar atmospherefor a predetermined period of time at a predetermined temperature (500°C.), thereby obtaining a sintered magnet (Nd—Fe—B sintered magnet).

In this embodiment, a description has been made of a uniaxialpressurizing system in which the molding direction is perpendicular tothe direction of magnetic field. Without being limited thereto, theremay be used a molding apparatus in which the molding direction is inparallel with the direction of the magnetic field. In addition, in thisembodiment, as the orientation magnetic field at the time of agitationand molding, there was used a static magnetic field in which theintensity per unit time of the magnetic field does not change. Withoutbeing limited thereto, there may be used, as shown in FIG. 6, a magneticpulse field in which the intensity of magnetic field per unit timevaries at a predetermined cycle. In this case, as shown in FIG. 7, itmay be so arranged that reverse magnetic field is charged.

According to this configuration, since vibrations can be applied to thealloy raw meal powder P at the time of agitation and molding of thealloy raw meals powder P, the orientation can further be improved. Inthis case, the period of pulse is preferably 1 ms˜2 and it is preferableto set the non-output time below 500 ms. If this range is exceeded,strong bonding chains will be broken, with the result that a highorientation cannot be obtained. In addition, in case the magnetic pulsefield is charged, the peak value shall preferably be set to 5˜50 kOe. Ifthe magnetic field intensity is weaker than 5 kOe, there cannot beobtained a product high in orientation and high in magnetic properties.On the other hand, if the magnetic field is stronger than 50 kOe, themagnetic field generating apparatus becomes too large to be practical.

In the embodiment, a description has been made of an example in which arotary vane 54 of screw vane type is used as the agitating means (rotaryagitation). However, without being limited thereto, there may be usedone in which a rectangular scoop (not illustrated) provided with adriving means such as a pneumatic cylinder is attached to a front end ofthe cylinder rod 52 a of the hydraulic cylinder 52 so as, in a state inwhich the scoop is buried into the alloy raw meal powder P, toreciprocate the scoop horizontally over the entire length in the radialdirection of the cavity 22 at a predetermined cycle (horizontalagitation). In this case, at the time of rotary agitation or horizontalagitation, the cylinder rod 52 a may be moved up and down so as to mixthe whole of the alloy raw meal powder P in the cavity 22.

Regarding the rotary vane 54 in the case of rotary agitation, as long asmixing can be made, during agitation, so as to mix the whole of thealloy raw meal powder P in the cavity 22, there is no particularlimitation. It may be of the type to generate air flow, but preferablyit shall be of a shape that hardly crushes the alloy raw meal powderduring agitation. As shown in FIG. 8, as the rotary vane, there may beemployed: a paddle vane type in which substantially L-shaped platepieces 54 a are provided on the rotary shaft while deviating by 90degrees (see FIG. 8( a)); a ribbon vane type in which vanes 54 b areprovided spirally (see FIG. 8( b)); and an anchor vane type in whichplate pieces 54 c are provided so as to extend horizontally relative tothe rotary shaft (see FIG. 8( c)). Depending on the selected rotaryvanes, the number of rotation and time of agitation are appropriatelyset. On the other hand, not only the rotary agitation and horizontalagitation as the agitation means, there may be employed one in which agas nozzle is provided at the front end of the cylinder rod 52 a tothereby constitute an agitating means made of a non-magnetic material. Ahigh-pressure gas may thus be intermittently or continuously ejected soas to agitate the alloy raw meal powder P in the cavity 22.

In the embodiment, a description has been made of an example in which auniaxial pressurizing type of compression molding apparatus 1 is used tomold the powder. Without being limited thereto, an isostatic moldingapparatus (not illustrated) using a rubber mold may be constituted. Inthis case, this rubber mold constituting the filling chamber is filledwith alloy raw meal powder P, and then an orienting step is performed toagitate in the magnetic field by the agitating apparatus 5. On the otherhand, there may be performed a second molding step in which the moldedbody M obtained by the molding step in the uniaxial pressurizing type ofcompression molding apparatus 1 is further molded by using the isostaticmolding apparatus. According to this configuration, the occurrence ofcracks and splits in the molded product can be reduced.

Further, in the embodiment, the compression molding apparatus 1 was usedto manufacture an oriented body by orienting in the magnetic field whileagitating the alloy raw meal powder P in the magnetic field.Subsequently, compression molding was executed in a state of chargingthe magnetic field. However, the following way may be employed. That is,the alloy raw meal powder that has been obtained in the above procedureis filled into a box body of Mo make having an upper opening and issubjected to agitation by the above-described agitating apparatus 5 fora predetermined period of time in a static magnetic field. Thereafter,the agitating apparatus 5 is retracted and, without demagnetizing, a lidof Mo make is mounted on the upper opening of the lid body. Thereafter,the magnetic field is attenuated and subsequently the box body with thelid mounted is placed as it is into a sintering furnace for sintering toobtain a permanent magnet (sintered body). In this case, the intensityof the magnetic field is set to 12 kOe, and the box body is formed intoa cube of 7 cm. And a sintered body was obtained by setting the numberof rotation of the agitating apparatus 5 to 40000 rpm and the time ofagitation to 2 seconds. As a result, average magnetic properties ofBr=15.01 kG, (BH) max=55.1 MG Oe and the degree of orientation of 99%were obtained.

Further, in the embodiment, a description has been made of an example ofmanufacturing a sintered magnet. However, this molding apparatus 1 canbe applied to manufacturing of an oriented body by orienting powderwhich polarizes in the magnetic field or electric field, and then bysubjecting this oriented body to compression molding. For example, therecan be listed the manufacturing of silicon nitride (Si₃N₄) by molding apredetermined powder in the magnetic field and then sintering it.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a molding apparatus for executing themethod of manufacturing according to this invention in a standbyposition;

FIG. 2 is a schematic view illustrating the operation of the moldingapparatus as shown in FIG. 1;

FIG. 3 is a schematic view illustrating the operation (orienting step)of the molding apparatus as shown in FIG. 1;

FIG. 4( a) is a schematic view illustrating the magnetic fieldorientation according to the conventional art, and FIG. 4( b) is aschematic view illustrating the agitating magnetic field orientation ofthis invention;

FIG. 5 is a schematic view illustrating the operation (molding step) ofthe molding apparatus as shown in FIG. 1;

FIG. 6 is a graph illustrating the magnetic pulse field;

FIG. 7 is a graph illustrating a modified example of the magnetic pulsefield; and

FIG. 8( a) through FIG. 8( c) are perspective views showing otherembodiments of rotary vanes to be used in an agitating apparatus.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1 compression molding apparatus    -   2 die    -   21 penetrating hole    -   22 cavity    -   31, 32 punches    -   4 magnetic field generating apparatus    -   5 agitating apparatus    -   54 rotary vane    -   53 lid plate    -   P alloy raw meal powder

1. A molding apparatus comprising: a filling chamber filled with powderthat is polarized in one of magnetic field and electric field; means forgenerating one of magnetic field and electric field so as to enable tocharge the powder filled in the filling chamber with one of the magneticfield and electric field; an agitating means for agitating and orientingthe powder in a state of being charged with one of the magnetic fieldand electric field; and a pressurizing means for applying a compressionforce in one of the magnetic field and electric field to the powder thathas been agitated and oriented, thereby molding the powder.
 2. Themolding apparatus according to claim 1, wherein the agitating means isdisposed in a manner to be movable into and out of the filling chamber.3. The molding apparatus according to claim 1, wherein the fillingchamber has an opening for filling the powder therethrough, and whereina lid body is provided integral with the agitating means in a manner toclose the opening when the agitating means is moved into the fillingchamber.
 4. The molding apparatus according to claim 1, wherein theagitating means is constituted by a non-magnetic material.
 5. Themolding apparatus according to claim 1, wherein the means for generatingthe magnetic field is capable of generating static magnetic field in arange of magnetic field intensity of 5˜30 kOe.
 6. The molding apparatusaccording to claim 1, wherein the means for generating the magneticfield is capable of generating magnetic pulse field in a range ofmagnetic field intensity of 5˜50 kOe.
 7. The molding apparatus accordingto claim 1, wherein the powder is alloy raw meal powder for rare-earthmagnet, the alloy raw meal powder being manufactured by quenchingmethod.
 8. The molding apparatus according to claim 2, wherein thefilling chamber has an opening for filling the powder therethrough, andwherein a lid body is provided integral with the agitating means in amanner to close the opening when the agitating means is moved into thefilling chamber.
 9. The molding apparatus according to claim 2, whereinthe agitating means is constituted by a non-magnetic material.